ui/base/models: Add empty() accessor to TreeNode class.

chrome/browser/ui/gtk/bookmarks/bookmark_bar_gtk.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/gtk/bookmarks/bookmark_bar_gtk.h"
 
 #include <vector>
 
 #include "base/metrics/histogram.h"
 #include "base/utf_string_conversions.h"
@@ skipping 513 matching lines @@
   }
 
   bookmark_utils::ConfigureButtonForNode(model_->other_node(),
       model_, other_bookmarks_button_, theme_service_);
 
   SetInstructionState();
   SetChevronState();
 }
 
 void BookmarkBarGtk::SetInstructionState() {
-  show_instructions_ = (model_->GetBookmarkBarNode()->child_count() == 0);
+  show_instructions_ = model_->GetBookmarkBarNode()->empty();
   if (show_instructions_) {
     gtk_widget_hide(bookmark_toolbar_.get());
     gtk_widget_show_all(instructions_);
   } else {
     gtk_widget_hide(instructions_);
     gtk_widget_show(bookmark_toolbar_.get());
   }
 }
 
 void BookmarkBarGtk::SetChevronState() {
@@ skipping 921 matching lines @@
 
   // Find the GtkWidget* for the actual target button.
   int shift = dir == GTK_MENU_DIR_PARENT ? -1 : 1;
   button_idx = (button_idx + shift + folder_list.size()) % folder_list.size();
   PopupForButton(folder_list[button_idx]);
 }
 
 void BookmarkBarGtk::CloseMenu() {
   current_context_menu_->Cancel();
 }